Apparatus for selectively sampling filter backwash fluid

ABSTRACT

This invention relates to monitoring apparatus and, in particular, but not exclusively to such apparatus for use in association with mains water supply facilities. A water works 10 has a water main 12, in which is located a filtration unit 13 having a filter 17. A pressure transducer 17a monitors the pressure drop across the filter 17 to initiate backwash. The conditions of backwash are monitored by a control unit 20 which operates valves 21 to 24 so that when abnormal conditions are detected a sample of the backwash fluid can be captured in reservoirs 25 to 27 in accordance with the degree of abnormality.

FIELD OF THE INVENTION

This invention relates to monitoring apparatus and, in particular, butnot exclusively, to such apparatus for use in association with mainswater supply facilities.

BACKGROUND OF THE INVENTION

There is ever increasing pressure on water companies to improve thequality of the water they supply and indeed any effluent they discharge.Whilst there are many sophisticated monitoring systems for detecting awhole range of pollutants, many of these do not work in real time and sosignificant discharges can occur from treatment plants before theproblem is discovered.

Very often a breakdown in the efficiency of the treatment plantfiltration system is indicated by an increase in solids in the water,but to date there is no method of monitoring such contaminants unlesstheir presence is in sufficient concentration to effect a change inturbidity and is thus detectable using a currently available instrument.

SUMMARY OF THE INVENTION

From one aspect the invention consists in apparatus for monitoring thelevel of solids in a fluid flow, comprising means for monitoring thelevel of contamination or blockage of a filter in the flow and fordeveloping an output signal if the level falls outside a predeterminedrange and means, responsive to the output signal, for sampling theresidue in the filter whenever an output signal is received.

Thus if the apparatus is used in conjunction with a filter positioned inthe output of a water treatment plant or in a sampling bypass thereof,then the need to backwash within a short time or the need for frequentbackwashing of that filter, or some other parameter, would indicate thatan unusually high level of solids was present in the outlet water fromthe treatment plant. This could immediately give rise to an alarm andaction could be taken to shut down the plant. The arrangement may havethe additional benefit that the treated water is subjected to a finalextra fine filtration providing an improvement in the quality of theoutput water if the total flow passes through the filter.

The output signal may also initiate an alarm and/or the recording ofpredetermined parameters. For example, a record may be kept of the timeof backwash, the elapsed time since the previous backwash, the flowthrough the filter and/or the pressure drop across the filter.Conveniently that record can be a printout.

In a preferred embodiment the apparatus includes means for backwashingthe filter, a normal backwash outlet and backwash sample reservoir andvalve means, responsive to the presence and absence of an output signal,for directing the backwash fluid to either the reservoir or the outletrespectively in dependence on the presence or absence of the outletsignal.

In a further embodiment the monitoring means may develop a differentoutput signal depending on in which of a plurality of predeterminedranges of levels the monitored level falls and wherein the samplingmeans characterises the sample by the nature of the output signal. Inthis case there may be a reservoir for each range and the valve meansmay be arranged to deliver the backwash fluid to that reservoir whichcorresponds to the output signal generated or to the normal outlet inthe absence of an output signal.

The output signal could be the absence of a `normal` signal or a changein level of that `normal` signal.

It will be understood that by capturing at least a sample of the residuewhich caused the unusual blocking of the filter the invention provides acompletely novel tool for the water engineer in allowing him todetermine the nature and significance of the fault in the upstream plantand to balance supplies from a variety of sources.

From another aspect the invention consists in apparatus for monitoringthe level of solids in a fluid flow and means for producing an alarmsignal when that level exceeds a predetermined level.

From a further aspect the invention consists in filter backwashapparatus comprising means for automatically backwashing a filter inresponse to a predetermined pressure drop across the filter and meansfor monitoring the time elapsed since the last backwash and/or thefrequency of backwash and for developing an output signal if the timeand/or frequency fall within a predetermined range.

BRIEF DESCRIPTION OF THE DRAWING

The invention may be performed in various ways and a specific embodimentwill now be described with reference to the accompanying drawing, whichis a schematic diagram of a water supply system including filterbackwash apparatus.

DETAILED DESCRIPTION OF THE INVENTION

Thus a water works, generally indicated at 10, has a large sand filter11, or indeed any source, from which water is supplied into a water main12. Before the water is passed to the consumer it can be fed through amonitoring unit 13, or possibly more usually, the monitoring unit 13 maycontinuously or intermittently sample the water in the main, if itsobject is simply to act as a monitoring system. Thus water from the mainis drawn along a pipe 14 by a pump 15 and is fed through a change-overvalve 16 to a filter 17. In normal operation the water passes throughthe filter 17 to an outlet 18.

As is well known in the filtration art, the pressure drop across thefilter elements in the filter A may be monitored, for example bypressure transducer 17a, and when this pressure drop indicates asignificant build up of solid material on the filter elements, thefilter 17 can be backwashed automatically by passing clean water throughthe filter 17 in a reverse direction.

A particularly convenient arrangement for achieving this is shown in thedrawing. Thus the apparatus includes a further filter 19 which, whenbackwash is required, can take a supply from the pump 15 via the valve16 and feed it in a reverse direction through the filter 17 so as tobackwash it. This filtering of the backwash water prevents a build up ofmaterial on the wrong side of the elements of the filter A.

In normal operation the indication of the need to backwash is noted by acontrol unit 20 which in turn opens a valve 22 allowing the backwashfluid to pass into a drain. The control unit 20 also records the timeand date at which that backwash occurs. When the apparatus subsequentlypasses into backwash, the control unit 20 calculates the time which haselapsed since the previous backwash and in dependence on that timedetermines the destination of the backwash fluid with its charge ofcontaminants.

This is achieved by providing a further three valves 22, 23 and 24 andselecting which of the valves 21 to 24 will be opened. As has alreadybeen mentioned, if 21 is opened the liquid simply passes to drain. If,however, one of the other valves is opened then the liquid passes into arespective reservoir 25 to 27. The selection of which valve 22 to 24 isopened can be made dependent on the time which has elapsed since theprevious backwash. Thus if, for example, less than four minutes hadelapsed valve 22 might be operated and a red alert warning alarm couldbe sounded. Similarly if the backwash occurs between four and thirtyminutes from the previous backwash valve 23 may be opened and an amberwarning could be given. If the backwash falls within the range thirty orsixty minutes then valve 24 may be opened and a green warning could begiven. Otherwise valve 21 is opened. Initial experiments have shown thatthese time ranges are viable, but other time ranges may also be useful.It will be understood that other sampling means may be used whichcapture all or a part of the residue backwash from the filter 17. Theabove described arrangement is, however, preferred because it preventscontaminated backwash fluid re-entering the supply system.

Thus the arrangement gives the water engineer an immediate indication ofthe level of the problem and also a sample of the material which hasactually resulted in the warning being given. Further if the problembuilds up over time he may have a profile of samples in the reservoirsas backwash becomes more frequent. This may particularly assist theengineer in charge in selecting his sources of water at any one time.

It is preferred that the control unit 20 also provides a writtenprintout 28 giving details of each and every backwash.

It will be understood that other parameters, other than elapsed time,can be used to produce a similar indication of rate of solid build up inthe filter A, for example frequency of backwash or the pressure dropacross the filter elements. Another possible parameter is the powerconsumption, or a factor hereof, of the pump 15. This will drop as thefilter becomes blocked. It will further be understood that warnings maybe visual, aural or any other suitable type. Other sampling arrangementsmay also be used. For example the backwash fluid may be diverted throughanother filter if an `alert` condition is detected.

Finally it will be appreciated that for the apparatus to be particularlyeffective, the filter elements and indeed the whole filter apparatus 17desirably operates in a highly repeatable manner, so that quite tightranges can be set. A particularly suitable filter element is describedin our International Patent Application No. PCT/GB90/01274.

The apparatus has been described in connection with water treatment. Itwill be understood that it is equally applicable to other installationswhere fluids which may contain contaminant solids need to be monitored.

I claim:
 1. Apparatus operable for monitoring the level of solids in afluid flow, comprising means for monitoring the level of contaminationof a filter in the flow and for developing an output signal if the levelfalls outside a predetermined range, means responsive to the outputsignal for sampling a sample residue in the filter whenever an outputsignal is received, means for backwashing the filter with a backwashingfluid, and a backwash outlet, said sampling means including a backwashsample reservoir and valve means, responsive to the presence of theoutput signal, for selectively directing backwash fluid that hasbackwashed the filter to either the backwash sample reservoir or thebackwash outlet respectively in dependence on the presence or absence ofthe output signal.
 2. Apparatus as claimed in claim 1, wherein themonitoring means includes means for developing a selected one ofdifferent output signals to constitute said output signal depending uponin which range of a plurality of ranges of level of contamination, themonitored level falls, and wherein the sampling means characterizes thesample by the nature of the output signal.
 3. Apparatus as claimed inclaim 2, further comprising a reservoir for each of said ranges, andwherein the valve means are arranged to deliver the sample to thereservoir corresponding to the respective one of signals developed or tothe backwash outlet in the absence of an output signal.
 4. Apparatus asclaimed in claim 1, wherein the means for backwashing automaticallybackwashes the filter in response to a predetermined pressure dropacross the filter, and the monitoring means further includes means formonitoring at least one of the time elapsed since the filter was lastbackwashed and the frequency of backwash.
 5. Apparatus as claimed inclaim 1, wherein the output signal initiates an alarm.
 6. Apparatus asclaimed in claim 1, wherein the output signal initiates a record ofpredetermined parameters.
 7. Apparatus as claimed in claim 6, whereinthe parameters include one or more of backwash time, elapsed time sincea previous backwash, flow through the filter or pressure drop across thefilter.
 8. Apparatus as claimed in claim 6, wherein the record is aprintout.